Hematopoietic stem cells and methods of treatment of neovascular eye diseases therewith

ABSTRACT

Isolated, mammalian, adult bone marrow-derived, lineage negative hematopoietic stem cell populations (Lin −  HSCs) contain endothelial progenitor cells (EPCs) capable of rescuing retinal blood vessels and neuronal networks in the eye. Preferably at least about 20% of the cells in the isolated Lin −  HSCs express the cell surface antigen CD 31 . The isolated Lin −  HSC populations are useful for treatment of ocular vascular diseases. In a preferred embodiment, the Lin −  HSCs are isolated by extracting bone marrow from an adult mammal; separating a plurality of monocytes from the bone marrow; labeling the monocytes with biotin-conjugated lineage panel antibodies to one or more lineage surface antigens; removing of monocytes that are positive for the lineage surface antigens from the plurality of monocytes, and recovering a Lin −  HSC population containing EPCs. Isolated Lin −  HSCs that have been transfected with therapeutically useful genes are also provided, and are useful for delivering genes to the eye for cell-based gene therapy. Methods of preparing isolated stem cell populations of the invention, and methods of treating ocular diseases and injury are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No. 10/833,743, filed on Apr. 28, 2004, now U.S. Pat. No. 7,838,290, which application is a continuation-in-part of U.S. patent application Ser. No. 10/628,783, filed on Jul. 25, 2003, now U.S. Pat. No. 7,153,501, which claims benefit of Provisional Patent Application No. 60/467,051, filed on May 2, 2003, and Provisional Patent Application No. 60/398,522, filed on Jul. 25, 2002 the entire disclosures of which are incorporated herein by reference

STATEMENT OF GOVERNMENT INTEREST

A portion of the work described herein was supported by grant number CA92577 from the National Cancer Institute and by grants number EY11254, EY12598 and EY125998 from the National Institutes of Health. The United States Government has certain rights in this invention.

FIELD OF THE INVENTION

This invention relates to isolated, mammalian, lineage negative hematopoietic stem cell (Lin⁻ HSC) populations derived from bone marrow and their uses. More particularly, the invention relates to isolated, mammalian, lineage negative hematopoietic stem cell (Lin⁻ HSC) populations containing endothelial progenitor cells (EPC). The invention also relates to treatment of vascular diseases of the eye by administering Lin⁻ HSC and transfected Lin⁻ HSC populations to the eye.

BACKGROUND OF THE INVENTION

Inherited degenerations of the retina affect as many as 1 in 3500 individuals and are characterized by progressive night blindness, visual field loss, optic nerve atrophy, arteriolar attenuation, altered vascular permeability and central loss of vision often progressing to complete blindness (Heckenlively, J. R., editor, 1988; Retinitis Pigmentosa, Philadelphia: JB Lippincott Co.). Molecular genetic analysis of these diseases has identified mutations in over 110 different genes accounting for only a relatively small percentage of the known affected individuals (Humphries et al., 1992, Science 256:804-808; Farrar et al. 2002, EMBO J. 21:857-864.). Many of these mutations are associated with enzymatic and structural components of the phototransduction machinery including rhodopsin, cGMP phosphodiesterase, rds peripherin, and RPE65. Despite these observations, there are still no effective treatments to slow or reverse the progression of these retinal degenerative diseases. Recent advances in gene therapy have led to successful reversal of the rds (Ali et al. 2000, Nat. Genet. 25:306-310) and rd (Takahashi et al. 1999, J. Virol. 73:7812-7816) phenotypes in mice and the RPE65 phenotype in dogs (Acland et al. 2001, Nat. Genet. 28:92-95) when the wild type transgene is delivered to photoreceptors or the retinal pigmented epithelium (RPE) in animals with a specific mutation.

Age related macular degeneration (ARMD) and diabetic retinopathy (DR) are the leading causes of visual loss in industrialized nations and do so as a result of abnormal retinal neovascularization. Since the retina consists of well-defined layers of neuronal, glial, and vascular elements, relatively small disturbances such as those seen in vascular proliferation or edema can lead to significant loss of visual function. Inherited retinal degenerations, such as retinitis pigmentosa (RP), are also associated with vascular abnormalities, such as arteriolar narrowing and vascular atrophy. While significant progress has been made in identifying factors that promote and inhibit angiogenesis, no treatment is currently available to specifically treat ocular vascular disease.

For many years it has been known that a population of stem cells exists in the normal adult circulation and bone marrow. Different sub-populations of these cells can differentiate along hematopoietic lineage positive (Lin⁺) or lineage negative (Lin⁻) lineages. Furthermore, the lineage negative hematopoietic stem cell (HSC) population has recently been shown to contain endothelial progenitor cells (EPC) capable of forming blood vessels in vitro and in vivo (See Asahara et al. 1997, Science 275: 964-7). These cells can participate in normal and pathological postnatal angiogenesis (See Lyden et al. 2001 Nat. Med. 7, 1194-201; Kalka et al. 2000, Proc. Natl. Acad. Sci. U.S.A. 97:3422-7; and Kocher et al. 2001, Nat. Med. 7: 430-6) as well as differentiate into a variety of non-endothelial cell types including hepatocytes (See Lagasse et al. 2000, Nat. Med. 6:1229-34), microglia (See Priller et al. 2002 Nat. Med. 7:1356-61), cardiomyocytes (See Orlic et al. 2001, Proc. Natl. Acad. Sci. U.S.A. 98: 10344-9) and epithelium (See Lyden et al. 2001, Nat. Med. 7:1194-1201). Although these cells have been used in several experimental models of angiogenesis, the mechanism of EPC targeting to neovasculature is not known and no strategy has been identified that will effectively increase the number of cells that contribute to a particular vasculature.

Hematopoietic stem cells from bone marrow are currently the only type of stem cell commonly used for therapeutic applications. Bone marrow HSC's have been used in transplants for over 40 years. Currently, advanced methods of harvesting purified stem cells are being investigated to develop therapies for treatment of leukemia, lymphoma, and inherited blood disorders. Clinical applications of stem cells in humans have been investigated for the treatment of diabetes and advanced kidney cancer in limited numbers of human patients.

SUMMARY OF THE INVENTION

The present invention provides isolated, mammalian, population of hematopoietic stem cells (HSCs) that do not express lineage surface antigens (Lin) on their cell surface, i.e, lineage negative hematopoietic stem cells (Lin⁻ HSCs). The Lin⁻ HSC populations of the present invention include endothelial progenitor cells (EPC), also known as endothelial precursor cells, that selectively target activated retinal astrocytes when intravitreally injected into the eye. The Lin⁻ HSCs of the present invention preferably are derived from adult mammalian bone marrow, more preferably from adult human bone marrow.

In a preferred embodiment the Lin⁻ HSC populations of the present invention are isolated by extracting bone marrow from an adult mammal; separating a plurality of monocytes from the bone marrow; labeling the monocytes with biotin-conjugated lineage panel antibodies to one or more lineage surface antigens, removing monocytes that are positive for the lineage surface antigens and then recovering a Lin⁻ HSC population containing EPCs. Preferably the monocytes are labeled with biotin-conjugated lineage panel antibodies to one or more lineage surface antigen selected from the group consisting of CD2, CD3, CD4, CD11, CD11a, Mac-1, CD14, CD16, CD19, CD24, CD33, CD36, CD38, CD45, Ly-6G, TER-119, CD45RA, CD56, CD64, CD68, CD86, CD66b, HLA-DR, and CD235a (Glycophorin A). Preferably, at least about 20% of the cells of the isolated Lin⁻ HSC population of the present invention express the surface antigen CD31.

The EPC's within the population of Lin⁻ HSCs of the present invention extensively incorporate into developing retinal vessels and remain stably incorporated into neovasculature of the eye. The isolated, Lin⁻ HSC populations of the present invention can be used to rescue and stabilize degenerating retinal vasculature in mammals, to rescue neuronal networks, and to facilitate repair of ischemic tissue.

In one preferred embodiment, the cells of the isolated Lin⁻ HSC populations are transfected with a therapeutically useful gene. For example, the cells can be transfected with polynucleotides that operably encode for neurotrophic agents or anti-angiogenic agents that selectively target neovasculature and inhibit new vessel formation without affecting already established vessels through a form of cell-based gene therapy. In one embodiment, the isolated, Lin⁻ HSC populations of the present invention include a gene encoding an angiogenesis inhibiting peptide. The angiogenesis inhibiting Lin⁻ HSCs are useful for modulating abnormal blood vessel growth in diseases such as ARMD, DR and certain retinal degenerations associated with abnormal vasculature. In another preferred embodiment, the isolated, Lin⁻ HSCs of the present invention include a gene encoding a neurotrophic peptide. The neurotrophic Lin⁻ HSCs are useful for promoting neuronal rescue in ocular diseases involving retinal neural degeneration, such as glaucoma, retinitis pigmentosa, and the like.

A particular advantage of ocular treatments with the isolated Lin⁻ HSC populations of the present invention is a vasculotrophic and neurotrophic rescue effect observed in eyes intravitreally treated with the Lin⁻ HSCs. Retinal neurons and photoreceptors are preserved and visual function is maintained in eyes treated with the isolated Lin⁻ HSCs of the invention. The present invention provides a method for treating retinal degeneration comprising administering isolated Lin⁻ HSC cells derived from bone marrow, which contain endothelial progenitor cells that selectively target activated retinal astrocytes, wherein at least about 50% the isolated Lin⁻ HSCs express the surface antigen CD31 and at least about 50% the isolated Lin⁻ HSCs express the surface antigen CD117 (c-kit).

The present invention also provides a method of isolating lineage negative hematopoietic stem cell populations containing endothelial progenitor cells from adult mammalian bone marrow, preferably from adult human bone marrow. In addition, a line of genetically identical cells (i.e., clones) can be generated from human Lin⁻ HSCs that are useful in regenerative or reparative treatment of retinal vasculature, as well as for treatment or amelioration of retinal neuronal tissue degeneration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (a and b) depicts schematic diagrams of developing mouse retina. (a) Development of primary plexus. (b) The second phase of retinal vessel formation. GCL, ganglion cell layer; IPL, inner plexus layer; INL, inner nuclear layer; OPL, outer plexus layer; ONL, outer nuclear layer; RPE, retinal pigment epithelium; ON, optic nerve; P, periphery.

FIG. 1 c depicts flow cytometric characterization of bone marrow-derived Lin⁺ HSC and Lin⁻ HSC separated cells. Top row: Dot plot distribution of non-antibody labeled cells, in which R1 defines the quantifiable-gated area of positive PE-staining; R2 indicates GFP-positive; Middle row: Lin⁻ HSC(C57B/6) and Bottom row: Lin⁺ HSC(C57B/6) cells, each cell line labeled with the PE-conjugated antibodies for Sca-1, c-kit, Flk-1/KDR, CD31. Tie-2 data was obtained from Tie-2-GFP mice. Percentages indicate percent of positive-labeled cells out of total Lin⁻ HSC or Lin⁺ HSC population.

FIG. 2 depicts engraftment of Lin⁻ HSCs into developing mouse retina. (a) At four days post-injection (P6) intravitreally injected eGFP Lin⁻ HSC cells attach and differentiate on the retina (b) Lin⁻ HSC (B6.129S7-Gtrosa26 mice, stained with β-gal antibody) establish themselves ahead of the vasculature stained with collagen IV antibody (asterisk indicates tip of vasculature). (c) Most of Lin⁺ HSC cells (eGFP⁺) at four days post-injection (P6) were unable to differentiate. (d) Mesenteric eGFP murine EC four days post-injection (P6). (e) Lin⁻ HSCs (eGFP⁺) injected into adult mouse eyes. (f) Low magnification of eGFP Lin⁻ HSCs (arrows) homing to and differentiating along the pre-existing astrocytic template in the GFAP-GFP transgenic mouse. (g) Higher magnification of association between Lin⁻ cells (eGFP) and underlying astrocyte (arrows). (h) Non-injected GFAP-GFP transgenic control. (i) Four days post-injection (P6), eGFP Lin⁻ HSCs migrate to and undergo differentiation in the area of the future deep plexus. Left figure captures Lin⁻ HSC activity in a whole mounted retina; right figure indicates location of the Lin⁻ cells (arrows) in the retina (top is vitreal side, bottom is scleral side). (j) Double labeling with α-CD31-PE and α-GFP-alexa 488 antibodies. Seven days after injection, the injected Lin⁻ HSCs (eGFP), red) were incorporated into the vasculature (CD31). Arrowheads indicate the incorporated areas. (k) eGFP Lin⁻ HSC cells form vessels fourteen days post-injection (P17). (l and m) Intra-cardiac injection of rhodamine-dextran indicates that the vessels are intact and functional in both the primary (l) and deep plexus (m).

FIG. 3 (a and b) shows that eGFP Lin⁻ HSC cells home to the gliosis (indicated by GFAP expressing-astrocytes, far left image) induced by both laser (a) and mechanical (b) induced injury in the adult retina (asterisk indicates injured site). Far right images are a higher magnification, demonstrating the close association of the Lin⁻ HSCs and astrocytes. Calibration bar=20 μM.

FIG. 4 shows that Lin⁻ HSC cells rescue the vasculature of the retinal degeneration mouse. (a-d) Retinas at 27 days post-injection (P33) with collagen IV staining; (a) and (b), retinas injected with Lin⁺ HSC cells (Balb/c) showed no difference in vasculature from normal FVB mice; (c) and (d) retinas injected with Lin⁻ HSCs (Balb/c) exhibited a rich vascular network analogous to a wild-type mouse; (a) and (c), frozen sections of whole retina (top is vitreal side, bottom is scleral side) with DAPI staining; (b) and (d), deep plexus of retinal whole amount; (e) bar graph illustrating the increase in vascularity of the deep vascular plexus formed in the Lin⁻ HSC cell-injected retinas (n=6). The extent of deep retinal vascularization was quantified by calculating the total length of vessels within each image. Average total length of vessels/high power field (in microns) for Lin⁻ HSC, Lin⁺ HSC or control retinas were compared. (f) Comparison of the length of deep vascular plexus after injection with Lin⁻ HSC (R, right eye) or Lin⁺ HSC (L, left eye) cells from rd/rd mouse. The results of six independent mice are shown (each color represents each mouse). (g) and (h) Lin⁻ HSC cells also (Balb/c) rescued the rd/rd vasculature when injected into P15 eyes. The intermediate and deep vascular plexus of Lin⁻ HSC (G) or Lin⁺ HSC (H) cell injected retinas (one month after injection) are shown.

FIG. 5 depicts photomicrographs of mouse retinal tissue: (a) deep layer of retinal whole mount (rd/rd mouse), five days post-injection (P11) with eGFP⁺ Lin⁻ HSCs visible (gray). (b) and (c) P60 retinal vasculature of Tie-2-GFP (rd/rd) mice that received Balb/c Lin⁻ cells (b) or Lin⁺ HSC cell (c) injection at P6. Only endogenous endothelial cells (GFP-stained) are visible in the left panels of (b) and (c). The middle panels of (b) and (c) are stained with CD31 antibody; arrows indicate the vessels stained with CD31 but not with GFP, the right panels of (b) and (c) show staining with both GFP and CD31. (d) α-SMA staining of Lin⁻ HSC injected (left panel) and control retina (right panel).

FIG. 6 shows that T2-TrpRS-transfected Lin⁻ HSCs inhibit the development of mouse retinal vasculature. (a) Schematic representation of human TrpRS, T2-TrpRS and T2-TrpRS with an Igk signal sequence at the amino terminus. (b) T2-TrpRS transfected Lin⁻ HSC-injected retinas express T2-TrpRS protein in vivo. (1) Recombinant T2-TrpRS produced in E. coli; (2) Recombinant T2-TrpRS produced in E. coli; (3) Recombinant T2-TrpRS produced in E. coli; (4) control retina; (5) Lin⁻ HSC+pSecTag2A (vector only) injected retina; (6) Lin⁻ HSC+pKLe135 (Igk-T2-TrpRS in pSecTag) injected retina. (a) Endogenous TrpRS. (b) Recombinant T2-TrpRS. (c) T2-TrpRS of Lin⁻ HSC injected retina. (c-f) Representative primary (superficial) and secondary (deep) plexuses of injected retinas, seven days post-injection; (c) and (d) Eyes injected with empty plasmid-transfected Lin⁻ HSC developed normally; (e) and (f) the majority of T2-TrpRS-transfected Lin⁻ HSC injected eyes exhibited inhibition of deep plexus; (c) and (e) primary (superficial) plexus; (d) and (f) secondary (deep) plexus). Faint outline of vessels observed in (f) are “bleed-through” images of primary network vessels shown in (e).

FIG. 7 shows the DNA sequence encoding His₆-tagged T2-TrpRS, SEQ ID NO: 1.

FIG. 8 shows the amino acid sequence of His₆-tagged T2-TrpRS, SEQ ID NO: 2.

FIG. 9 illustrates photomicrographs and electroretinograms (ERG) of retinas from mice whose eyes were injected with the Lin⁻ HSC of the present invention and with Lin⁺ HSC (controls).

FIG. 10 depicts statistical plots showing a correlation between neuronal rescue (y-axis) and vascular rescue x-axis) for both the intermediate (Int.) and deep vascular layers of rd/rd mouse eyes treated with Lin⁻ HSC.

FIG. 11 depicts statistical plots showing no correlation between neuronal rescue (y-axis) and vascular rescue x-axis) for rd/rd mouse eyes that were treated with Lin⁺ HSC.

FIG. 12 is a bar graph of vascular length (y-axis) in arbitrary relative units for rd/rd mouse eyes treated with the Lin⁻ HSC (dark bars) and untreated (light bars) rd/rd mouse eyes at time points of 1 month (1M), 2 months (2M), and 6 months (6M) post-injection.

FIG. 13 includes three bar graphs of the number of nuclei in the outer neural layer (ONR) of rd/rd mice at 1 month (1M), 2 months (2M) and 6 months (6M), post-injection, and demonstrates a significant increase in the number of nuclei for eyes treated with Lin⁻ HSC (dark bars) relative to control eyes treated with Lin⁺ HSC (light bars).

FIG. 14 depicts plots of the number of nuclei in the outer neural layer for individual rd/rd mice, comparing the right eye (R, treated with Lin⁻ HSC) relative to the left eye (L, control eye treated with Lin⁺ HSC) at time points (post injection) of 1 month (1M), 2 months (2M), and 6 months (6M); each line in a given plot compares the eyes of an individual mouse.

FIG. 15 depicts retinal vasculature and neural cell changes in rd1/rd1 (C3H/HeJ, left panels) or wild type mice (C57BL/6, right panels). Retinal vasculature of intermediate (upper panels) or deep (middle panels) vascular plexuses in whole-mounted retinas (red: collagen IV, green: CD31) and sections (red: DAPI, green: CD31, lower panels) of the same retinas are shown (P: postnatal day). (GCL: ganglion cell layer, INL: inter nuclear layer, ONL: outer nuclear layer).

FIG. 16 shows that Lin⁻ HSC injection rescues the degeneration of neural cells in rd1/rd1 mice. A, B and C, retinal vasculature of intermediate (int.) or deep plexus and sections of Lin⁻ HSC injected eye (right panels) and contralateral control cell (CD31⁻) injected eye (left panels) at P30 (A), P60 (B), and P180 (C). D, the average total length of vasculature (+ or − standard error of the mean) in Lin⁻ HSC injected or control cell (CD31⁻) injected retinas at P30 (left, n=10), P60 (middle, n=10), and P180 (right, n=6). Data of intermediate (Int.) and deep vascular plexus are shown separately (Y axis: relative length of vasculature). E, the average numbers of cell nuclei in the ONL at P30 (left, n=10), P60 (middle, n=10), or P180 (right, n=6) of control cell (CD31⁻) or Lin⁻ HSC injected retinas (Y axis: relative number of cell nuclei in the ONL). F, Linear correlations between the length of vasculature (X axis) and the number of cell nuclei in the ONL (Y axis) at P30 (left), P60 (middle), and P180 (right) of Lin⁻ HSC or control cell injected retinas.

FIG. 17 demonstrates that retinal function is rescued by Lin⁻ HSC injection. Electroretinographic (ERG) recordings were used to measure the function of Lin⁻ HSC or control cell (CD31⁻) injected retinas. A and B, Representative cases of rescued and non-rescued retinas 2 months after injection. Retinal section of Lin⁻ HSC injected right eye (A) and CD31⁻ control cell injected left eye (B) of the same animal are shown (green: CD31 stained vasculature, red: DAPI stained nuclei). C, ERG results from the same animal shown in A & B.

FIG. 18 shows that a population of human bone marrow cells can rescue degenerating retinas in the rd1 mouse (A-C). The rescue is also observed in another model of retinal degeneration, rd10 (D-K). A, human Lin⁻ HSCs (hLin⁻HSCs) labeled with green dye can differentiate into retinal vascular cells after intravitreal injection into C3SnSmn. CB17-Prkdc SCID mice. B and C, Retinal vasculature (left panels; upper: intermediate plexus, lower: deep plexus) and neural cells (right panel) in hLin⁻ HSC injected eye (B) or contralateral control eye (C) 1.5 months after injection. D-K, Rescue of rd10 mice by Lin⁻ HSCs (injected at P6). Representative retinas at P21 (D: Lin⁻ HSCs, H: control cells), P30 (E: Lin⁻ HSCs, I: control cells), P60 (F: Lin⁻ HSCs, J: control cells), and P105 (G: Lin⁻ HSCs, K: control cells) are shown (treated and control eyes are from the same animal at each time point). Retinal vasculature (upper image in each panel is the intermediate plexus; the middle image in each panel is the deep plexus) was stained with CD31 (green) and Collagen IV (red). The lower image in each panel shows a cross section made from the same retina (red: DAPI, green: CD31).

FIG. 19 demonstrates that crystallin αA is up regulated in rescued outer nuclear layer cells after treatment with Lin⁻ HSCs but not in contralateral eyes treated with control cells. Left panel; IgG control in rescued retina, Middle panel; crystallin αA in rescued retina, Right panel; crystallin αA in non-rescued retina.

FIG. 20 includes tables of genes that are upregulated in murine retinas that have been treated with the Lin⁻ HSCs of the present invention. (A) Genes whose expression is increased 3-fold in mouse retinas treated with murine Lin⁻ HSCs. (B) Crystallin genes that are upregulated in mouse retinas treated with murine Lin⁻ HSC. (C) Genes whose expression is increased 2-fold in mouse retinas treated with human Lin⁻ HSCs. (D) Genes for neurotrophic factors or growth factors whose expression is upregulated in mouse retinas treated with human Lin⁻ HSCs.

FIG. 21 illustrates the distribution of CD31 and integrin α6 surface antigens on CD133 positive (DC133⁺) and CD133 negative (CD133⁻) human Lin⁻ HSC populations of the present invention.

FIG. 22 illustrates postnatal retinal development in wild-type C57/B16 mice raised in normal oxygen levels (normoxia), at post natal days P0 through P30.

FIG. 23 illustrates oxygen-induced retinopathy model in C57/B16 mice raised in high oxygen levels (hyperoxia; 75% oxygen) between P7 and P12, followed by normoxia from P12-P17.

FIG. 24 demonstrates vascular rescue by treatment with the Lin⁻ HSC populations of the present invention in the oxygen-induced retinopathy model.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Stem cells are typically identified by the distribution of antigens on the surface of the cells (for a detailed discussion see Stem Cells: Scientific Progress and Future Directions, a report prepared by the National Institutes of Health, Office of Science Policy, June 2001, Appendix E: Stem Cell Markers, which is incorporated herein by reference to the extent pertinent).

Hematopoietic stem cells are that stem cells that are capable of developing into various blood cell types e.g., B cells, T cells, granulocytes, platelets, and erythrocytes. The lineage surface antigens are a group of cell-surface proteins that are markers of mature blood cell lineages, including CD2, CD3, CD11, CD11a, Mac-1 (CD11b:CD18), CD14, CD16, CD19, CD24, CD33, CD36, CD38, CD45, CD45RA, murine Ly-6G, murine TER-119, CD56, CD64, CD68, CD86 (B7.2), CD66b, human leucocyte antigen DR(HLA-DR), and CD235a (Glycophorin A). Hematopoietic stem cells that do not express significant levels of these antigens are commonly referred to a lineage negative (Lin⁻). Human hematopoietic stem cells commonly express other surface antigens such as CD31, CD34, CD117 (c-kit) and/or CD133. Murine hematopoietic stem cells commonly express other surface antigens such as CD34, CD117 (c-kit), Thy-1, and/or Sca-1.

The present invention provides isolated hematopoietic stem cells that do not express significant levels of a ‘lineage surface antigen’ (Lin) on their cell surfaces. Such cells are referred to herein as ‘lineage negative’ or ‘Lin⁻’ hematopoietic stem cells. In particular this invention provides a population of Lin⁻ hematopoietic stems cells (Lin⁻ HSCs) that include endothelial progenitor cells (EPCs), which are capable of incorporating into developing vasculature and then differentiating to become vascular endothelial cells. Preferably the isolated Lin⁻ HSC populations are present in a culture medium such as phosphate buffered saline (PBS).

As used herein and in the appended claims, the phrase ‘adult’ in reference to bone marrow, includes bone marrow isolated postnatally, i.e., from juvenile and adult individuals, as opposed to embryos. The term ‘adult mammal’ refers to both juvenile and fully mature mammals.

The present invention provides isolated, mammalian, lineage negative hematopoietic stem cell (Lin⁻ HSC) populations containing endothelial progenitor cells (EPCs). The isolated Lin⁻ HSC populations of the present invention preferably comprise mammalian cells in which at least about 20% of the cells express the surface antigen CD31, which is commonly present on endothelial cells. In other embodiment, at least about 50% of the cells express CD31, more preferably at least about 65%, most preferably at least about 75%. Preferably at least about 50% of the cells of the Lin⁻ HSC populations of the present invention preferably express the integrin α6 antigen.

In one preferred murine Lin⁻ HSC population embodiment, at least about 50% of the cells express CD31 antigen and at least about 50% of the cells express the CD117 (c-kit) antigen. Preferably, at least about 75% of the Lin⁻ HSC cells express the surface antigen CD31, more preferably about 81% of the cells. In another preferred murine embodiment, at least about 65% of the cells express the surface antigen CD117, more preferably about 70% of the cells. A particularly preferred embodiment of the present invention is a population of murine Lin⁻ HSCs in which about 50% to about 85% of the cells express the surface antigen CD31 and about 70% to about 75% of the cells express the surface antigen CD117.

Another preferred embodiment is a human Lin⁻ HSC population in which the cells are CD133 negative, in which at least about 50% of the cells express the CD31 surface antigen and at least about 50% of the cells express the integrin α6 antigen. Yet another preferred embodiment is a human Lin⁻ HSC population in which the cells are CD133 positive, in which at less than about 30% of the cells express the CD31 surface antigen and less than about 30% of the cells express the integrin α6 antigen.

The isolated Lin⁻ HSC populations of the present invention selectively target astrocytes and incorporate into the retinal neovasculature when intravitreally injected into the eye of the mammalian species, such as a mouse or a human, from which the cells were isolated.

The isolated Lin⁻ HSC populations of the present invention include endothelial progenitor cells that differentiate to endothelial cells and generate vascular structures within the retina. In particular, the Lin⁻ HSC populations of the present invention are useful for the treatment of retinal neovascular and retinal vascular degenerative diseases, and for repair of retinal vascular injury. The Lin⁻ HSC cells of the present invention promote neuronal rescue in the retina and promote upregulation of anti-apoptotic genes. It has surprisingly been found that adult human Lin⁻ HSC cells of the present invention can inhibit retinal degeneration even in severe combined immunodeficient (SCID) mice suffering from retinal degeneration. Additionally, the Lin⁻ HSC populations can be utilized to treat retinal defects in the eyes of neonatal mammals, such as mammals suffering from oxygen induced retinopathy or retinopathy of prematurity.

The present invention also provides a method of treating ocular diseases in a mammal comprising isolating from the bone marrow of the mammal a lineage negative hematopoietic stem cell population that includes endothelial progenitor cells, and intravitreally injecting the isolated stem cells into an eye of the mammal in a number sufficient to arrest the disease. The present method can be utilized to treat ocular diseases such as retinal degenerative diseases, retinal vascular degenerative diseases, ischemic retinopathies, vascular hemorrhages, vascular leakage, and choroidopathies in neonatal, juvenile or fully mature mammals. Examples of such diseases include age related macular degeneration (ARMD), diabetic retinopathy (DR), presumed ocular histoplasmosis (POHS), retinopathy of prematurity (ROP), sickle cell anemia, and retinitis pigmentosa, as well as retinal injuries.

The number of stem cells injected into the eye is sufficient for arresting the disease state of the eye. For example, the number of cells can be effective for repairing retinal damage of the eye, stabilizing retinal neovasculature, maturing retinal neovasculature, and preventing or repairing vascular leakage and vascular hemorrhage.

Cells of the Lin⁻ HSC populations of the present invention can be transfected with therapeutically useful genes, such as genes encoding antiangiogenic proteins for use in ocular, cell-based gene therapy and genes encoding neurotrophic agents to enhance neuronal rescue effects.

The transfected cells can include any gene which is therapeutically useful for treatment of retinal disorders. In one preferred embodiment, the transfected Lin⁻ HSCs of the present invention include a gene operably encoding an antiangiogenic peptide, including proteins, or protein fragments such as TrpRS or antiangiogenic fragments thereof, e.g., the T1 and T2 fragments of TrpRS, which are described in detail in co-owned, co-pending U.S. patent application Ser. No. 10/080,839, the disclosure of which is incorporated herein by reference. The transfected Lin⁻ HSCs encoding an antiangiogenic peptide of the present invention are useful for treatment of retinal diseases involving abnormal vascular development, such as diabetic retinopathy, and like diseases. Preferably the Lin⁻ HSCs are human cells.

In another preferred embodiment, the transfected Lin⁻ HSCs of the present invention include a gene operably encoding a neurotrophic agent such as nerve growth factor, neurotrophin-3, neurotrophin-4, neurotrophin-5, ciliary neurotrophic factor, retinal pigmented epithelium-derived neurotrophic factor, insulin-like growth factor, glial cell line-derived neurotrophic factor, brain-derived neurotrophic factor, and the like. Such neurotrophic Lin⁻ HSCs are useful for promoting neuronal rescue in retinal neuronal degenerative diseases such as glaucoma and retinitis pigmentosa, in treatment of injuries to the retinal nerves, and the like. Implants of ciliary neurotrophic factor have been reported as useful for the treatment of retinitis pigmentosa (see Kirby et al. 2001, Mol. Ther. 3(2):241-8; Farrar et al. 2002, EMBO Journal 21:857-864). Brain-derived neurotrophic factor reportedly modulates growth associated genes in injured retinal ganglia (see Fournier, et al., 1997, J. Neurosci. Res. 47:561-572). Glial cell line derived neurotrophic factor reportedly delays photoreceptor degeneration in retinitis pigmentosa (see McGee et al. 2001, Mol. Ther. 4(6):622-9).

The present invention also provides a method of isolating a lineage negative hematopoietic stem cells comprising endothelial progenitor cells from bone marrow of a mammal. The method entails the steps of (a) extracting bone marrow from an adult mammal; (b) separating a plurality of monocytes from the bone marrow; (c) labeling the monocytes with biotin-conjugated lineage panel antibodies to one or more lineage surface antigens, preferably lineage surface antigens selected from the group consisting of CD2, CD3, CD4, CD11, CD11a, Mac-1, CD14, CD16, CD19, CD24, CD33, CD36, CD38, CD45, Ly-6G (murine), TER-119 (murine), CD45RA, CD56, CD64, CD68, CD86 (B7.2), CD66b, human leucocyte antigen DR(HLA-DR), and CD235a (Glycophorin A); (d) removing monocytes that are positive for said one or more lineage surface antigens from the plurality of monocytes and recovering a population of lineage negative hematopoietic stem cells containing endothelial progenitor cells, preferably in which at least about 20% of the cells express CD31.

When the Lin⁻ HSC are isolated from adult human bone marrow, preferably the monocytes are labeled with biotin-conjugated lineage panel antibodies to lineage surface antigens CD2, CD3, CD4, CD11a, Mac-1, CD14, CD16, CD19, CD33, CD38, CD45RA, CD64, CD68, CD86 (B7.2), and CD235a. When the Lin⁻ HSC are isolated from adult murine bone marrow, preferably the monocytes are labeled with biotin-conjugated lineage panel antibodies to lineage surface antigens CD3, CD11, CD45, Ly-6G, and TER-119.

In a preferred method, the cells are isolated from adult human bone marrow and are further separated by CD133 lineage. One preferred method of isolating human Lin⁻ HSCs includes the additional steps of labeling the monocytes with a biotin-conjugated CD133 antibody and recovering a CD133 positive, Lin⁻ HSC population. Typically, less than about 30% of such cells express CD31 and less than about 30% of such cell express integrin α6. The human Cd133 positive, Lin⁻ HSC populations of the present invention can target sites of peripheral ischemia-driven neovascularization when injected into eyes that are not undergoing angiogenesis.

Another preferred method of isolating human Lin⁻ HSCs includes the additional steps of labeling the monocytes with a biotin-conjugated CD133 antibody, removing CD133 positive cells, and recovering a CD133 negative, Lin⁻ HSC population. Typically, at least about 50% of such cells express CD31 and at least about 50% of such cell express integrin α6. The human CD133 negative, Lin⁻ HSC populations of the present invention can incorporate into developing vasculature when injected into eyes that are undergoing angiogenesis.

The present invention also provides methods for treating ocular angiogenic diseases by administering transfected Lin⁻ HSC cells of the present invention by intravitreal injection of the cells into the eye. Such transfected Lin⁻ HSC cells comprise Lin⁻ HSC transfected with a therapeutically useful gene, such as a gene encoding antiangiogenic or neurotrophic gene product. Preferably the transfected Lin⁻ HSC cells are human cells.

Preferably, at least about 1×10⁵ Lin⁻ HSC cells or transfected Lin⁻ HSC cells are administered by intravitreal injection to a mammalian eye suffering from a retinal degenerative disease. The number of cells to be injected may depend upon the severity of the retinal degeneration, the age of the mammal and other factors that will be readily apparent to one of ordinary skill in the art of treating retinal diseases. The Lin⁻ HSC may be administered in a single dose or by multiple dose administration over a period of time, as determined by the clinician in charge of the treatment.

The Lin⁻ HSCs of the present invention are useful for the treatment of retinal injuries and retinal defects involving an interruption in or degradation of the retinal vasculature or retinal neuronal degeneration. Human Lin⁻ HSCs also can be used to generate a line of genetically identical cells, i.e., clones, for use in regenerative or reparative treatment of retinal vasculature, as well as for treatment or amelioration of retinal neuronal degeneration.

METHODS Example 1 Cell Isolation and Enrichment; Preparation of Murine Lin⁻ HSC Populations A and B

General Procedure. All in vivo evaluations were performed in accordance with the NIH Guide for the Care and Use of Laboratory Animals, and all evaluation procedures were approved by The Scripps Research Institute (TSR1, La Jolla, Calif.) Animal Care and Use Committee. Bone marrow cells were extracted from B6.129S7-Gtrosa26, Tie-2GFP, ACTbEGFP, FVB/NJ (rd/rd mice) or Balb/cBYJ adult mice (The Jackson Laboratory, ME).

Monocytes were then separated by density gradient separation using HISTOPAQUE™ polysucrose gradient (Sigma, St. Louis, Mo.) and labeled with biotin conjugated lineage panel antibodies (CD45, CD3, Ly-6G, CD11, TER-119, Pharmingen, San Diego, Calif.) for Lin⁻ selection in mice. Lineage positive (Lin⁺) cells were separated and removed from Lin⁻ HSC using a magnetic separation device (AUTOMACS™ sorter, Miltenyi Biotech, Auburn, Calif.). The resulting Lin⁻ HSC population, containing endothelial progenitor cells was further characterized using a FACS™ Calibur flow cytometer (Becton Dickinson, Franklin Lakes, N.J.) using following antibodies: PE-conjugated-Sca-1, c-kit, KDR, and CD31 (Pharmingen, San Diego, Calif.). Tie-2-GFP bone marrow cells were used for characterization of Tie-2.

To harvest adult mouse endothelial cells, mesenteric tissue was surgically removed from ACTbEGFP mouse and placed in collagenase (Worthington, Lakewood, N.J.) to digest the tissue, followed by filtration using a 45 μm filter. Flow-through was collected and incubated with Endothelial Growth Media (Clonetics, San Diego, Calif.). Endothelial characteristics were confirmed by observing morphological cobblestone appearance, staining with CD31 mAb (Pharmingen) and examining cultures for the formation of tube-like structures in MATRIGEL™ matrix (Beckton Dickinson, Franklin Lakes, N.J.).

Murine Lin⁻ HSC Population A. Bone marrow cells were extracted from ACTbEGFP mice by the General Procedure described above. The Lin⁻ HSC cells were characterized by FACS flow cytometry for CD31, c-kit, Sca-1, Flk-1, and Tie-2 cell surface antigen markers. The results are shown in FIG. 1 c. About 81% of the Lin⁻ HSC exhibited the CD31 marker, about 70.5% of the Lin⁻ HSC exhibited the c-kit marker, about 4% of the Lin⁻ HSC exhibited the Sca-1 marker, about 2.2% of the Lin⁻ HSC exhibited the Flk-1 marker and about 0.91% of the Lin⁻ HSC cell exhibited the Tie-2 marker. In contrast, the Lin⁺ HSC that were isolated from these bone marrow cells had a significantly different cell marker profile (i.e., CD31: 37.4%; c-kit: 20%; Sca-1: 2.8%; Flk-: 0.05%).

Murine Lin⁻HSC Population B. Bone marrow cells were extracted from Balb/C, ACTbEGFP, and C3H mice by the General Procedure described above. The Lin⁻ HSC cells were analyzed for the presence of cell surface markers (Sca-1, KDR, c-kit, CD34, CD31 and various integrins: α1, α2, α3, α4, α5, α6, α_(M), α_(V), α_(X), α_(IIb), β₁, β₄, β₃, β₄, β₅ and β₇). The results are shown in Table 1.

TABLE 1 Characterization of Lin⁻ HSC Population B. Cell Marker Lin⁻ HSC α1 0.10 α2 17.57 α3 0.22 α4 89.39 α5 82.47 α6 77.70 αL 62.69 αM 35.84 αX 3.98 αV 33.64 αIIb 0.25 β1 86.26 β2 49.07 β3 45.70 β4 0.68 β5 9.44 β7 11.25 CD31 51.76 CD34 55.83 Flk-1/KDR 2.95 c-kit (CD117) 74.42 Sca-1 7.54

Example 2 Intravitreal Administration of Cells in a Murine Model

An eyelid fissure was created in a mouse eyelid with a fine blade to expose the P2 to P6 eyeball. Lineage negative HSC Population A of the present invention (approximately 10⁵ cells in about 0.5 μl to about 1 μl of cell culture medium) was then injected intravitreally using a 33-gauge (Hamilton, Reno, Nev.) needled-syringe.

Example 3 EPC Transfection

Murine Lin⁻ HSC (Population A) were transfected with DNA encoding the T2 fragment of TrpRS also enclosing a His₆ tag (SEQ ID NO: 1, FIG. 7) using FuGENE™6 Transfection Reagent (Roche, Indianapolis, Ind.) according to manufacturer's protocol. Lin⁻ HSC cells (about 10⁶ cell per ml) were suspended in opti-MEM™ medium (Invitrogen, Carlsbad, Calif.) containing stem cell factor (PeproTech, Rocky Hill, N.J.). DNA (about 1 μg) and FuGENE reagent (about 3 μl) mixture was then added, and the mixtures were incubated at about 37° C. for about 18 hours. After incubation, cells were washed and collected. The transfection rate of this system was approximately 17% that was confirmed by FACS analysis. T2 production was confirmed by western blotting. The amino acid sequence of His₆-tagged T2-TrpRS is shown as SEQ ID NO: 2, FIG. 8.

Example 4 Immunohistochemistry and Confocal Analysis

Mouse retinas were harvested at various time points and were prepared for either whole mounting or frozen sectioning. For whole mounts, retinas were fixed with 4% paraformaldehyde, and blocked in 50% fetal bovine serum (FBS) and 20% normal goat serum for one hour at ambient room temperature. Retinas were processed for primary antibodies and detected with secondary antibodies. The primaries used were: anti-Collagen IV (Chemicon, Temecula, Calif., anti-β-gal (Promega, Madison, Wis.), anti-GFAP (Dako Cytomation, Carpenteria, Calif.), anti-α-smooth muscle actin (α-SMA, Dako Cytomation). Secondary antibodies used were conjugated either to Alexa 488 or 594 fluorescent markers (Molecular Probes, Eugene, Oreg.). Images were taken using an MRC 1024 Confocal microscope (Bio-Rad, Hercules, Calif.). Three-dimensional images were created using LASERSHARP™ software (Bio-Rad) to examine the three different layers of vascular development in the whole mount retina. The difference in GFP pixel intensity between enhanced GFP (eGFP) mice and GFAP/wtGFP mice, distinguished by confocal microscopy, was utilized to create the 3D images.

Example 5 In vivo Retinal Angiogenesis Quantification Assay in Mice

For T2-TrpRS analysis, the primary and deep plexus were reconstructed from the three dimensional images of mouse retinas. The primary plexus was divided into two categories: normal development, or halted vascular progression. The categories of inhibition of deep vascular development were construed based upon the percentage of vascular inhibition including the following criteria: complete inhibition of deep plexus formation was labeled ‘Complete’, normal vascular development (including less than 25% inhibition) was labeled ‘Normal’ and the remainder labeled ‘Partial.’ For the rd/rd mouse rescue data, four separate areas of the deeper plexus in each whole mounted retina were captured using a 10× lens. The total length of vasculature was calculated for each image, summarized and compared between the groups. To acquire accurate information, Lin⁻ HSC were injected into one eye and Lin⁺ HSC into another eye of the same mouse. Non-injected control retinas were taken from the same litter.

Example 6 Adult Retinal Injury Murine Models

Laser and scar models were created using either a diode laser (150 mW, 1 second, 50 mm) or mechanically by puncturing the mouse retina with a 27 gauge needle. Five days after injury, cells were injected using the intravitreal method. Eyes were harvested from the mice five days later.

Example 7 Neurotrophic Rescue of Retinal Regeneration

Adult murine bone marrow derived lineage negative hematopoietic stem cells (Lin⁻ HSC) have a vasculotrophic and neurotrophic rescue effect in a mouse model of retinal degeneration. Right eyes of 10-day old mice were injected intravitreally with about 0.5 microliters containing about 10⁵ Lin⁻ HSC of the present invention and evaluated 2 months later for the presence of retinal vasculature and neuronal layer nuclear count. The left eyes of the same mice were injected with about the same number of Lin⁺ HSC as a control, and were similarly evaluated. As shown in FIG. 9, in the Lin⁻ HSC treated eyes, the retinal vasculature appeared nearly normal, the inner nuclear layer was nearly normal and the outer nuclear layer (ONL) had about 3 to about 4 layers of nuclei. In contrast, the contralateral Lin⁺ HSC treated eye had a markedly atrophic middle retinal vascular layer, a completely atrophic outer retinal vascular layer; the inner nuclear layer was markedly atrophic and the outer nuclear layer was completely gone. This was dramatically illustrated in Mouse 3 and Mouse 5. In Mouse 1, there was no rescue effect and this was true for approximately 15% of the injected mice.

When visual function was assessed with electroretinograms (ERG), the restoration of a positive ERG was observed when both the vascular and neuronal rescue was observed (Mice 3 and 5). Positive ERG was not observed when there was no vascular or neuronal rescue (Mouse 1). This correlation between vascular and neurotrophic rescue of the rd/rd mouse eyes by the Lin⁻ HSC of the present invention is illustrated by a regression analysis plot shown in FIG. 10. A correlation between neuronal (y-axis) and vascular α-axis) recovery was observed for the intermediate vasculature type (r=0.45) and for the deep vasculature (r=0.67).

FIG. 11 shows the absence of any statistically significant correlation between vascular and neuronal rescue by Lin⁺ HSC. The vascular rescue was quantified and the data are presented in FIG. 12. Data for mice at 1 month (1M), 2 months (2M), and 6 months (6M), post-injection shown in FIG. 12, demonstrate that vascular length was significantly increased in eyes treated with the Lin⁻ HSC of the present invention (dark bars) relative to the vascular length in untreated eyes from the same mouse (light bars), particularly at 1 month and 2 months, post-injection. The neurotrophic rescue effect was quantified by counting nuclei in the inner and outer nuclear layers about two months after injection of Lin⁻ HSC or Lin⁺ HSC. The results are presented in FIGS. 13 and 14.

Example 8 Human Lin⁻ HSC Population

Bone marrow cells were extracted from healthy adult human volunteers by the General Procedure described above. Monocytes were then separated by density gradient separation using HISTOPAQUE™ polysucrose gradient (Sigma, St. Louis, Mo.). To isolate the Lin⁻ HSC population from human bone marrow mononuclear cells the following biotin conjugated lineage panel antibodies were used with the magnetic separation system (AUTOMACS™ sorter, Miltenyi Biotech, Auburn, Calif.): CD2, CD3, CD4, CD11a, Mac-1, CD14, CD16, CD19, CD33, CD38, CD45RA, CD64, CD68, CD86, CD235a (Pharmingen).

The human Lin⁻ HSC population was further separated into two sub-populations based on CD133 expression. The cells were labeled with biotin-conjugated CD133 antibodies ans separated into CD133 positive and CD133 negative sub-populations.

Example 9 Intravitreal Administration of Human and Murine Cells in Murine Models for Retinal Degeneration

C3H/HeJ, C3SnSmn.CB17-Prkdc SCID, and rd10 mouse strains were used as retinal degeneration models. C3H/HeJ and C3SnSmn.CB17-Prkdc SCID mice (The Jackson Laboratory, Maine) were homozygous for the retinal degeneration 1 (rd1) mutation, a mutation that causes early onset severe retinal degeneration. The mutation is located in exon 7 of the Pde6b gene encoding the rod photoreceptor cGMP phosphodiesterase β subunit. The mutation in this gene has been found in human patients with autosomal recessive retinitis pigmentosa (RP). C3SnSmn.CB17-Prkdc SCID mice are also homozygous for the severe combined immune deficiency spontaneous mutation (Prkdc SCID) and were used for human cell transfer experiments. Retinal degeneration in rd10 mice is caused by a mutation in exon 13 of Pde6b gene. This is also a clinically relevant RP model with later onset and milder retinal degeneration than rd1/rd1). All evaluations were performed in accordance with the NIH Guide for the Care and Use of Laboratory Animals, and all procedures were approved by The Scripps Research Institute Animal Care and Use Committee.

An eyelid fissure was created in a mouse eyelid with a fine blade to expose the P2 to P6 eyeball. Lineage negative HSC cells for murine population A or human population C (approximately 10⁵ cells in about 0.5 μl to about 1 μl of cell culture medium) were then injected in the mouse eye intravitreally using a 33-gauge (Hamilton, Reno, Nev.) needled-syringe. To visualize the injected human cells, cells were labeled with dye (Cell tracker green CMFDA, Molecular Probes) before injection.

Retinas were harvested at various time points and fixed with 4% paraformaldehyde (PFA) and methanol followed by blocking in 50% FBS/20% NGS for one hour at room temperature. To stain retinal vasculature, retinas were incubated with anti-CD31 (Pharmingen) and anti-collagen IV (Chemicon) antibodies followed by Alexa 488 or 594 conjugated secondary antibodies (Molecular Probes, Eugene, Oreg.). The retinas were laid flat with four radial relaxing incisions to obtain a whole mount preparation. Images of vasculature in intermediate or deep retinal vascular plexuses (see Dorrell et al. 2002 Invest Ophthalmol. Vis. Sci. 43:3500-3510) were obtained using a Radiance MP2100 confocal microscope and LASERSHARP™ software (Biorad, Hercules, Calif.). For quantification of vasculature, four independent fields (900 μm×900 μm) were chosen randomly from the mid portion of the intermediate or deep vascular layer and the total length of vasculature was measured using LASERPIX™ analyzing software (Biorad). The total lengths of these four fields in the same plexus were used for further analysis.

The flat-mounted retinas were re-embedded for cryostat sections. Retinas were placed in 4% PFA overnight followed by incubation with 20% sucrose. The retinas were embedded in optimal cutting temperature compound (OCT: Tissue-Tek; Sakura FineTech, Torrance, Calif.). Cryostat sections (10 μm) were re-hydrated in PBS containing the nuclear dye DAPI (Sigma-Aldrich, St. Louis, Mo.). DAPI-labeled nuclear images of three different areas (280 μm width, unbiased sampling) in a single section that contained optic nerve head and the entire peripheral retina were taken by confocal microscope. The numbers of the nuclei located in ONL of the three independent fields in one section were counted and summed up for analysis. Simple linear-regression analysis was performed to examine the relationship between the length of vasculature in the deep plexus and the number of cell nuclei in the ONL.

Following overnight dark-adaptation, mice were anesthetized by intraperitoneal injection of 15 μg/gm ketamine and 7 μg/gm xylazine. Electroretinograms (ERGs) were recorded from the corneal surface of each eye after pupil dilation (1% atropine sulfate) using a gold loop corneal electrode together with a mouth reference and tail ground electrode. Stimuli were produced with a Grass Photic Stimulator (PS33 Plus, Grass Instruments, Quincy, Mass.) affixed to the outside of a highly reflective Ganzfeld dome. Rod responses were recorded to short-wavelength (Wratten 47A; λ_(max)=470 nm) flashes of light over a range of intensities up to the maximum allowable by the photic stimulator (0.668 cd-s/m²). Response signals were amplified (CP511 AC amplifier, Grass Instruments), digitized (PCI-1200, National Instruments, Austin, Tex.) and computer-analyzed. Each mouse served as its own internal control with ERGs recorded from both the treated and untreated eyes. Up to 100 sweeps were averaged for the weakest signals. The averaged responses from the untreated eye were digitally subtracted from the responses from the treated eye and this difference in signal was used to index functional rescue.

Microarray analysis was used for evaluation of Lin⁻ HSC-targeted retinal gene expression. P6 rd/rd mice were injected with either Lin⁻ or CD31⁻ HSCs. The retinas of these mice were dissected 40 days post-injection in RNase free medium (rescue of the retinal vasculature and the photoreceptor layer is obvious at this time point after injection). One quadrant from each retina was analyzed by whole mount to ensure that normal HSC targeting as well as vasculature and neural protection had been achieved. RNA from retinas with successful injections was purified using a TRIzol (Life Technologies, Rockville, Md.), phenol/chloroform RNA isolation protocol. RNA was hybridized to Affymetrix Mu74Av2 chips and gene expression was analyzed using GENESPRING™ software (SiliconGenetics, Redwood City, Calif.). Purified human or mouse HSCs were injected intravitreally into P6 mice. At P45 the retinas were dissected and pooled into fractions of 1) human HSC-injected, rescued mouse retinas, 2) human HSC-injected, non-rescued mouse retinas, and 3) mouse HSC-injected, rescued mouse retinas for purification of RNA and hybridization to human-specific U133A Affymetrix chips. GENESPRING™ software was used to identify genes that were expressed above background and with higher expression in the human HSC-rescued retinas. The probe-pair expression profiles for each of these genes were then individually analyzed and compared to a model of normal human U133A microarray experiments using dChip to determine human species specific hybridization and to eliminate false positives due to cross-species hybridization.

When the CD133 positive and CD133 negative Lin⁻ HSC sub-population was intravitreally injected into the eyes of neonatal SCID mice, the greatest extent of incorporation into the developing vasculature was observed for the CD133 negative sub-population, which expresses both CD31 and integrin α6 surface antigens (see FIG. 21, bottom). The CD133 positive sub-population, which does not express CD31 or integrin α6 (FIG. 21, top) appears to target sites of peripheral ischemia-driven neovascularization, but not when injected into eyes undergoing angiogenesis.

Example 10 Intravitreal Administration of Murine Cells in Murine Models for Oxygen Induced Retinal Degeneration

New born wild-type C57B16 mice were exposed to hyperoxia (75% oxygen) between postnatal days P7 to P12 in an oxygen-induced retinal degeneration (OIR) model. FIG. 22 illustrates normal postnatal vascular development in C57B16 mice from P0 to P30. At P0 only budding superficial vessels can be observed around the optic disc. Over the next few days, the primary superficial network extends toward the periphery, reaching the far periphery by day P10. Between P7 and P12, the secondary (deep) plexus develops. By P17, an extensive superficial and deep network of vessels is present (FIG. 22, insets). In the ensuing days, remodeling occurs along with development of the tertiary (intermediate) layer of vessels until the adult structure is reached approximately at P21.

In contrast, in the OIR model, following exposure to 75% oxygen at P7-P12, the normal sequence of events is severely disrupted (FIG. 23). Adult murine Lin⁻ HSC populations of the invention were intravitreally injected at P3 in an eye of a mouse that was subsequently subjected to OIR, the other eye was injected with PBS or CD31 negative cells as a control. FIG. 24 illustrates that the Lin⁻ HSC populations of the present invention can reverse the degenerative effects of high oxygen levels in the developing mouse retina. Fully developed superficial and deep retinal vasculature was observed at P17 in the treated eyes, whereas in the control eyes showed large avascular areas with virtually no deep vessels (FIG. 24). Approximately 100 eyes of mice in the OIR model were observed. Normal vascularization was observed in 58% of the eyes treated with the Lin⁻ HSC populations of the invention, compared to 12% of the control eyes treated with CD31⁻ cells and 3% of the control eyes treated with PBS.

RESULTS Murine Retinal Vascular Development; A Model for Ocular Angiogenesis

The mouse eye provides a recognized model for the study of mammalian retinal vascular development, such as human retinal vascular development. During development of the murine retinal vasculature, ischemia-driven retinal blood vessels develop in close association with astrocytes. These glial elements migrate onto the third trimester human fetus, or the neonatal rodent, retina from the optic disc along the ganglion cell layer and spread radially. As the murine retinal vasculature develops, endothelial cells utilize this already established astrocytic template to determine the retinal vascular pattern (See FIGS. 1 a and b). FIG. 1 (a and b) depicts schematic diagrams of developing mouse retina. FIG. 1 a depicts development of the primary plexus (dark lines at upper left of the diagram) superimposed over the astrocyte template (light lines) whereas, FIG. 1 b depicts the second phase of retinal vessel formation. In the Figures, GCL stands for ganglion cell layer; IPL stands for inner plexus layer; INL stands for inner nuclear layer; OPL stands for outer plexus layer; ONL stands for outer nuclear layer; RPE stands for retinal pigment epithelium; ON stands for optic nerve; and P stands for periphery.

At birth, retinal vasculature is virtually absent. By postnatal day 14 (P14) the retina has developed complex primary (superficial) and secondary (deep) layers of retinal vessels coincident with the onset of vision. Initially, spoke-like peripapillary vessels grow radially over the pre-existing astrocytic network towards the periphery, becoming progressively interconnected by capillary plexus formation. These vessels grow as a monolayer within the nerve fiber through P10 (FIG. 1 a). Between P7-P8 collateral branches begin to sprout from this primary plexus and penetrate into the retina to the outer plexiform layer where they form the secondary, or deep, retinal plexus. By P21, the entire network undergoes extensive remodeling and a tertiary, or intermediate, plexus forms at the inner surface of inner nuclear layer (FIG. 1 b).

The neonatal mouse retinal angiogenesis model is useful for studying the role of HSC during ocular angiogenesis for several reasons. In this physiologically relevant model, a large astrocytic template exists prior to the appearance of endogenous blood vessels, permitting an evaluation of the role for cell-cell targeting during a neovascular process. In addition, this consistent and reproducible neonatal retinal vascular process is known to be hypoxia-driven, in this respect having similarities to many retinal diseases in which ischemia is known to play a role.

Enrichment of Endothelial Progenitor Cells (EPC) From Bone Marrow

Although cell surface marker expression has been extensively evaluated on the EPC population found in preparations of HSC, markers that uniquely identify EPC are still poorly defined. To enrich for EPC, hematopoietic lineage marker positive cells (Lin⁺), i.e., B lymphocytes (CD45), T lymphocytes (CD3), granulocytes (Ly-6G), monocytes (CD11), and erythrocytes (TER-119), were depleted from bone marrow mononuclear cells of mice. Sca-1 antigen was used to further enrich for EPC. A comparison of results obtained after intravitreal injection of identical numbers of either Lin⁻ Sca-1⁺ cells or Lin⁻ cells, no difference was detected between the two groups. In fact, when only Lin⁻ Sca-1⁻ cells were injected, far greater incorporation into developing blood vessels was observed.

The Lin⁻ HSC populations of the present invention are enriched with EPCs, based on functional assays. Furthermore, Lin⁺ HSC populations functionally behave quite differently from the Lin⁻ HSC populations. Epitopes commonly used to identify EPC for each fraction (based on previously reported in vitro characterization studies) were also evaluated. While none of these markers were exclusively associated with the Lin⁻ fraction, all were increased about 70 to about 1800% in the Lin⁻ HSC, compared to the Lin⁺ HSC fraction (FIG. 1 c). FIG. 1 c illustrates flow cytometric characterization of bone marrow-derived Lin⁺ HSC and Lin⁻ HSC separated cells. The top row of FIG. 1 c shows a hematopoietic stem cell dot plot distribution of non-antibody labeled cells. R1 defines the quantifiable-gated area of positive PE-staining; R2 indicates GFP-positive. Dot plots of Lin⁻ HSC are shown in the middle row and dot plots of Lin⁺ HSC are shown in the bottom row. The C57B/6 cells were labeled with the PE-conjugated antibodies for Sca-1, c-kit, Flk-1/KDR, CD31. Tie-2 data was obtained from Tie-2-GFP mice. The percentages in the corners of the dot plots indicate the percent of positive-labeled cells out of total Lin⁻ or Lin⁺ HSC population. Interestingly, accepted EPC markers like Flk-1/KDR, Tie-2, and Sca-1 were poorly expressed and, thus, not used for further fractionation.

Intravitreally Injected HSC Lin⁻ Cells Contain EPC That Target Astrocytes and Incorporate into Developing Retinal Vasculature

To determine whether intravitreally injected Lin⁻ HSC can target specific cell types of the retina, utilize the astrocytic template and participate in retinal angiogenesis, approximately 10⁵ cells from a Lin⁻ HSC composition of the present invention or Lin⁺ HSC cells (control, about 10⁵ cells) isolated from the bone marrow of adult (GFP or LacZ transgenic) mice were injected into postnatal day 2 (P2) mouse eyes. Four days after injection (P6), many cells from the Lin⁻ HSC composition of the present invention, derived from GFP or LacZ transgenic mice were adherent to the retina and had the characteristic elongated appearance of endothelial cells (FIG. 2 a). FIG. 2 illustrates engraftment of Lin cells into developing mouse retina. As shown in FIG. 2 a, the four days post-injection (P6) intravitreally injected eGFP+Lin⁻ HSC attach and differentiate on the retina.

In many areas of the retinas, the GFP-expressing cells were arranged in a pattern conforming to underlying astrocytes and resembled blood vessels. These fluorescent cells were observed ahead of the endogenous, developing vascular network (FIG. 2 b). Conversely, only a small number of Lin⁺ HSC (FIG. 2 c), or adult mouse mesenteric endothelial cells (FIG. 2 d) attached to the retinal surface. In order to determine whether cells from an injected Lin⁻ HSC population could also attach to retinas with already established vessels, we injected a Lin⁻ HSC composition into adult eyes. Interestingly, no cells were observed to attach to the retina or incorporate into established, normal retinal blood vessels (FIG. 2 e). This indicates that the Lin⁻ HSC compositions of the present invention do not disrupt a normally developed vasculature and will not initiate abnormal vascularization in normally developed retinas.

In order to determine the relationship between an injected Lin⁻ HSC compositions of the present invention and retinal astrocytes, a transgenic mouse was used, which expressed glial fibrillary acidic protein (GFAP, a marker of astrocytes) and promoter-driven green fluorescent protein (GFP). Examination of retinas of these GFAP-GFP transgenic mice injected with Lin⁻ HSC from eGFP transgenic mice demonstrated co-localization of the injected eGFP EPC and existing astrocytes (FIG. 2 f-h, arrows). Processes of eGFP+Lin⁻ HSC were observed to conform to the underlying astrocytic network (arrows, FIG. 2 g). Examination of these eyes demonstrated that the injected, labeled cells only attached to astrocytes; in P6 mouse retinas, where the retinal periphery does not yet have endogenous vessels, injected cells were observed adherent to astrocytes in these not yet vascularized areas. Surprisingly, injected, labeled cells were observed in the deeper layers of the retina at the precise location where normal retinal vessels will subsequently develop (FIG. 2 i, arrows).

To determine whether injected Lin⁻ HSC of the present invention are stably incorporated into the developing retinal vasculature, retinal vessels at several later time points were examined. As early as P9 (seven days after injection), Lin⁻ HSC incorporated into CD31⁺ structures (FIG. 2 j). By P16 (14 days after injection), the cells were already extensively incorporated into retinal vascular-like structures (FIG. 2 k). When rhodamine-dextran was injected intravascularly (to identify functional retinal blood vessels) prior to sacrificing the animals, the majority of Lin⁻ HSC were aligned with patent vessels (FIG. 21). Two patterns of labeled cell distribution were observed: (1) in one pattern, cells were interspersed along vessels in between unlabeled endothelial cells; and (2) the other pattern showed that vessels were composed entirely of labeled cells. Injected cells were also incorporated into vessels of the deep vascular plexus (FIG. 2 m). While sporadic incorporation of Lin⁻ HSC-derived EPC into neovasculature has been previously reported, this is the first report of vascular networks being entirely composed of these cells. This demonstrates that cells from a population of bone marrow-derived Lin⁻ HSC of the present invention injected intravitreally can efficiently incorporate into any layer of the forming retinal vascular plexus.

Histological examination of non-retinal tissues (e.g., brain, liver, heart, lung, bone marrow) did not demonstrate the presence of any GFP positive cells when examined up to 5 or 10 days after intravitreal injection. This indicates that a sub-population of cells within the Lin⁻ HSC fraction selectively target to retinal astrocytes and stably incorporate into developing retinal vasculature. Since these cells have many characteristics of endothelial cells (association with retinal astrocytes, elongate morphology, stable incorporation into patent vessels and not present in extravascular locations), these cells represent EPC present in the Lin⁻ HSC population. The targeted astrocytes are of the same type observed in many of the hypoxic retinopathies. It is well known that glial cells are a prominent component of neovascular fronds observed in DR and other forms of retinal injury. Under conditions of reactive gliosis and ischemia-induced neovascularization, activated astrocytes proliferate, produce cytokines, and up-regulate GFAP, similar to that observed during neonatal retinal vascular template formation in many mammalian species including humans.

Lin⁻ HSC populations of the present invention will target activated astrocytes in adult mouse eyes as they do in neonatal eyes, Lin⁻ HSC cells were injected into adult eyes with retinas injured by photo-coagulation (FIG. 3 a) or needle tip (FIG. 3 b). In both models, a population of cells with prominent GFAP staining was observed only around the injury site (FIGS. 3 a and b). Cells from injected Lin⁻ HSC compositions localized to the injury site and remained specifically associated with GFAP-positive astrocytes (FIGS. 3 a and b). At these sites, Lin⁻ HSC cells were also observed to migrate into the deeper layer of retina at a level similar to that observed during neonatal formation of the deep retinal vasculature. Uninjured portions of retina contained no Lin⁻ HSC cells, identical to that observed when Lin⁻ HSC were injected into normal, uninjured adult retinas (FIG. 2 e). These data indicate that Lin⁻ HSC compositions can selectively target activated glial cells in injured adult retinas with gliosis as well as neonatal retinas undergoing vascularization.

Intravitreally Injected Lin⁻ HSC Can Rescue and Stabilize Degenerating Vasculature

Since intravitreally injected Lin⁻ HSC compositions target astrocytes and incorporate into the normal retinal vasculature, these cells also stabilize degenerating vasculature in ischemic or degenerative retinal diseases associated with gliosis and vascular degeneration. The rd/rd mouse is a model for retinal degeneration that exhibits profound degeneration of photoreceptor and retinal vascular layers by one month after birth. The retinal vasculature in these mice develops normally until P16 at which time the deeper vascular plexus regresses; in most mice the deep and intermediate plexuses have nearly completely degenerated by P30.

To determine whether HSC can rescue the regressing vessels, Lin⁺ or Lin⁻ HSC (from Balb/c mice) were injected into rd/rd mice intravitreally at P6. By P33, after injection with Lin⁺ cells, vessels of the deepest retinal layer were nearly completely absent (FIGS. 4 a and b). In contrast, most Lin⁻ HSC-injected retinas by P33 had a nearly normal retinal vasculature with three parallel, well-formed vascular layers (FIGS. 4 a and 4 d). Quantification of this effect demonstrated that the average length of vessels in the deep vascular plexus of Lin injected rd/rd eyes was nearly three times greater than untreated or Lin⁺ cell-treated eyes (FIG. 4 e). Surprisingly, injection of a Lin⁻ HSC composition derived from rd/rd adult mouse (FVB/N) bone marrow also rescued degenerating rd/rd neonatal mouse retinal vasculature (FIG. 40. Degeneration of the vasculature in rd/rd mouse eyes in observed as early as 2-3 weeks post-natally. Injection of Lin⁻ HSC as late as P15 also resulted in partial stabilization of the degenerating vasculature in the rd/rd mice for at least one month (FIGS. 4 g and 4 h).

A Lin⁻ HSC composition injected into younger (e.g., P2) rd/rd mice also incorporated into the developing superficial vasculature. By P11, these cells were observed to migrate to the level of the deep vascular plexus and form a pattern identical to that observed in the wild type outer retinal vascular layer (FIG. 5 a). In order to more clearly describe the manner in which cells from injected Lin⁻ HSC compositions incorporate into, and stabilize, degenerating retinal vasculature in the rd/rd mice, a Lin⁻ HSC composition derived from Balb/c mice was injected into Tie-2-GFP FVB mouse eyes. The FVB mice have the rd/rd genotype and because they express the fusion protein Tie-2-GFP, all endogenous blood vessels are fluorescent.

When non-labeled cells from a Lin⁻ HSC composition are injected into neonatal Tie-2-GFP FVB eyes and are subsequently incorporated into the developing vasculature, there should be non-labeled gaps in the endogenous, Tie-2-GFP labeled vessels that correspond to the incorporated, non-labeled Lin⁻ HSC that were injected. Subsequent staining with another vascular marker (e.g., CD-31) then delineates the entire vessel, permitting determination as to whether non-endogenous endothelial cells are part of the vasculature. Two months after injection, CD31-positive, Tie-2-GFP negative, vessels were observed in the retinas of eyes injected with the Lin⁻ HSC composition (FIG. 5 b). Interestingly, the majority of rescued vessels contained Tie-2-GFP positive cells (FIG. 5 c). The distribution of pericytes, as determined by staining for smooth muscle actin, was not changed by Lin⁻ HSC injection, regardless of whether there was vascular rescue (FIG. 5 d). These data clearly demonstrate that intravitreally injected Lin⁻ HSC compositions of the present invention migrate into the retina, participate in the formation of normal retinal blood vessels, and stabilize endogenous degenerating vasculature in a genetically defective mouse.

Inhibition of Retinal Angiogenesis by Transfected Cells from Lin⁻ HSC

The majority of retinal vascular diseases involve abnormal vascular proliferation rather than degeneration. Transgenic cells targeted to astrocytes can be used to deliver an anti-angiogenic protein and inhibit angiogenesis. Cells from Lin⁻ HSC compositions were transfected with T2-tryptophanyl-tRNA synthetase (T2-TrpRS). T2-TrpRS is a 43 kD fragment of TrpRS that potently inhibits retinal angiogenesis (FIG. 6 a). On P12, retinas of eyes injected with a control plasmid-transfected Lin⁻ HSC composition (no T2-TrpRS gene) on P2 had normal primary (FIG. 6 c) and secondary (FIG. 6 d) retinal vascular plexuses. When the T2-TrpRS transfected Lin⁻ HSC composition of the present invention was injected into P2 eyes and evaluated 10 days later, the primary network had significant abnormalities (FIG. 6 e) and formation of the deep retinal vasculature was nearly completely inhibited (FIG. 6 f). The few vessels observed in these eyes were markedly attenuated with large gaps between vessels. The extent of inhibition by T2-TrpRS-secreting Lin⁻ HSCs is detailed in Table 2.

T2-TrpRS is produced and secreted by cells in the Lin⁻ HSC composition in vitro and after injection of these transfected cells into the vitreous, a 30 kD fragment of T2-TrpRS in the retina (FIG. 6 b) was observed. This 30 kD fragment was specifically observed only in retinas injected with transfected Lin⁻ HSC of the present invention and this decrease in apparent molecular weight compared to the recombinant or in vitro-synthesized protein may be due to processing or degradation of the T2-TrpRS in vivo. These data indicate that Lin⁻ HSC compositions can be used to deliver functionally active genes, such as genes expressing angiostatic molecules, to the retinal vasculature by targeting to activated astrocytes. While it is possible that the observed angiostatic effect is due to cell-mediated activity this is very unlikely since eyes treated with identical, but non-T2-transfected Lin⁻ HSC compositions had normal retinal vasculature.

TABLE 2 Vascular Inhibition by T2-TrpRS-secreting Lin⁻ HSCs Primary Plexus Deep Plexus Inhibited Normal Complete Partial Normal TsTrpRs 60% 40% 33.3% 60% 6.7% (15 eyes) (9 eyes)  (6 eyes) (5 eyes) (9 eyes) (1 eye) Control  0% 100%    0% 38.5%   61.5%  (13 eyes) (0 eyes) (13 eyes) (0 eyes) (5 eyes) (8 eyes)

Intravitreally injected Lin⁻ HSC populations localize to retinal astrocytes, incorporate into vessels, and can be useful in treating many retinal diseases. While most cells from injected HSC compositions adhere to the astrocytic template, small numbers migrate deep into the retina, homing to regions where the deep vascular network will subsequently develop. Even though no GFAP-positive astrocytes were observed in this area prior to 42 days postnatally, this does not rule out the possibility that GFAP-negative glial cells are already present to provide a signal for Lin⁻ HSC localization. Previous studies have shown that many diseases are associated with reactive gliosis. In DR, in particular, glial cells and their extracellular matrix are associated with pathological angiogenesis.

Since cells from injected Lin⁻ HSC compositions specifically attached to GFAP-expressing glial cells, regardless of the type of injury, Lin⁻ HSC compositions of the present invention can be used to target pre-angiogenic lesions in the retina. For example, in the ischemic retinopathies such as diabetes, neovascularization is a response to hypoxia. By targeting Lin⁻ HSC compositions to sites of pathological neovascularization, developing neovasculature can be stabilized preventing abnormalities of neovasculature such as hemorrhage or edema (the causes of vision loss associated with DR) and can potentially alleviate the hypoxia that originally stimulated the neovascularization. Abnormal blood vessels can be restored to normal condition. Furthermore, angiostatic proteins, such as T2-TrpRS can be delivered to sites of pathological angiogenesis by using transfected Lin⁻ HSC compositions and laser-induced activation of astrocytes. Since laser photocoagulation is a commonly used in clinical ophthalmology, this approach has application for many retinal diseases. While such cell-based approaches have been explored in cancer therapy, their use for eye diseases is more advantageous since intraocular injection makes it possible to deliver large numbers of cells directly to the site of disease.

Neurotrophic and Vasculotrophic Rescue by Lin⁻ HSC

MACS was used to separate Lin⁻ HSC from bone marrow of enhanced green fluorescent protein (eGFP), C3H (rd/rd), FVB (rd/rd) mice as described above. Lin⁻ HSC containing EPC from these mice were injected intravitreally into P6 C3H or FVB mouse eyes. The retinas were collected at various time points (1 month, 2 months, and 6 months) after injection. The vasculature was analyzed by scanning laser confocal microscope after staining with antibodies to CD31 and retinal histology after nuclear staining with DAPI. Microarray gene expression analysis of mRNA from retinas at varying time points was also used to identify genes potentially involved in the effect.

Eyes of rd/rd mice had profound degeneration of both neurosensory retina and retinal vasculature by P21. Eyes of rd/rd mice treated with Lin⁻ HSC on P6 maintained a normal retinal vasculature for as long as 6 months; both deep and intermediate layers were significantly improved when compared to the controls at all timepoints (1M, 2M, and 6M) (see FIG. 12). In addition, we observed that retinas treated with Lin⁻ HSC were also thicker (1M; 1.2-fold, 2M; 1.3-fold, 6M; 1.4-fold) and had greater numbers of cells in the outer nuclear layer (1 M; 2.2-fold, 2M; 3.7-fold, 6M; 5.7-fold) relative to eyes treated with Lin⁺ HSC as a control. Large scale genomic analysis of ‘rescued’ (e.g., Lin⁻ HSC) compared to control (untreated or non-Lin⁻ treated) rd/rd retinas demonstrated a significant upregulation of genes encoding sHSPs (small heat shock proteins) and specific growth factors that correlated with vascular and neural rescue, including genes encoding the proteins listed in FIG. 20, panels A and B.

The bone marrow derived Lin⁻ HSC populations of the present invention significantly and reproducibly induced maintenance of a normal vasculature and dramatically increased photoreceptor and other neuronal cell layers in the rd/rd mouse. This neurotrophic rescue effect correlated with significant upregulation of small heat shock proteins and growth factors and provides insights into therapeutic approaches to currently untreatable retinal degenerative disorders.

Rd1/rd1 Mouse Retinas Exhibit Profound Vascular and Neuronal Degeneration.

Normal postnatal retinal vascular and neuronal development in mice has been well described and is analogous to changes observed in the third trimester human fetus (Dorrell et al., 2002, Invest. Ophthalmol. Vis. Sci. 43:3500-3510). Mice homozygous for the rd1 gene share many characteristics of human retinal degeneration (Frasson et al., 1999, Nat. Med. 5:1183-1187) and exhibit rapid photoreceptor (PR) loss accompanied by severe vascular atrophy as the result of a mutation in the gene encoding PR cGMP phosphodiesterase (Bowes et al. 1990, Nature 347:677-680). To examine the vasculature during retinal development and its subsequent degeneration, antibodies against collagen IV (CIV), an extracellular matrix (ECM) protein of mature vasculature, and CD31 (PECAM-1), a marker for endothelial cells were used (FIG. 15). Retinas of rd1/rd1 (C3H/HeJ) developed normally until approximately postnatal day (P) 8 when degeneration of the photoreceptor-containing outer nuclear layer (ONL) began. The ONL rapidly degenerated and cells died by apoptosis such that only a single layer of nuclei remained by P20. Double staining of the whole-mounted retinas with antibodies to both CIV and CD31 revealed details of the vascular degeneration in rd1/rd1 mice similar to that described by others (Blanks et al., 1986, J. Comp. Neurol. 254:543-553). The primary and deep retinal vascular layers appeared to develop normally though P12 after which there is a rapid loss of endothelial cells as evidenced by the absence of CD31 staining. CD31 positive endothelial cells were present in a normal distribution through P12 but rapidly disappeared after that. Interestingly, CIV positive staining remained present throughout the time points examined, suggesting that the vessels and associated ECM formed normally, but only the matrix remained after P13 by which time no CD31 positive cells were observed. (FIG. 15, middle panels). The intermediate vascular plexus also degenerates after P21, but the progression is slower than that observed in the deep plexus (FIG. 15, upper panel). Retinal vascular and neural cell layers of a normal mouse are shown for comparison to the rd1/rd1 mouse (right panels, FIG. 15).

Neuroprotective Effect of Bone Marrow-Derived Lin⁻ HSCs in rd1/rd1 Mice.

Intravitreally injected Lin⁻ HSCs incorporate into endogenous retinal vasculature in all three vascular plexuses and prevent the vessels from degenerating. Interestingly, the injected cells are virtually never observed in the outer nuclear layer. These cells either incorporate into the forming retinal vessels or are observed in close proximity to these vessels. Murine Lin⁻ HSCs (from C3H/HeJ) were intravitreally injected into C3H/HeJ (rd1/rd1) mouse eyes at P6, just prior to the onset of degeneration. By P30, control cell (CD31⁻)-injected eyes exhibited the typical rd1/rd1 phenotype, i.e., nearly complete degeneration of the deep vascular plexus and ONL was observed in every retina examined. Eyes injected with Lin⁻ HSCs maintained normal-appearing intermediate and deep vascular plexuses. Surprisingly, significantly more cells were observed in the internuclear layer (INL) and ONL of Lin⁻ HSC-injected eyes than in control cell-injected eyes (FIG. 16A). This rescue effect of Lin⁻ HSCs could be observed at 2 months (FIG. 16B) and for as long as 6 months after injection (FIG. 16C). Differences in the vasculature of the intermediate and deep plexuses of Lin⁻ HSC-injected eyes, as well as the neuronal cell-containing INL and ONL, were significant at all time points measured when rescued and non-rescued eyes were compared (FIGS. 16B and C). This effect was quantified by measuring the total length of the vasculature (FIG. 16D) and counting the number of DAPI-positive cell nuclei observed in the ONL (FIG. 16E). Simple linear-regression analysis was applied to the data at all time points.

A statistically significant correlation was observed between vascular rescue and neuronal (e.g., ONL thickness) rescue at P30 (p<0.024) and P60 (p<0.034) in the Lin⁻ HSC-injected eyes (FIG. 16F). The correlation remained high, although not statistically significant (p<0.14) at P180 when comparing Lin⁻ HSC-injected retinas to control cell-injected retinas (FIG. 16F). In contrast, control cell-injected retinas showed no significant correlation between the preservation of vasculature and ONL at any time point (FIG. 16F). These data demonstrate that intravitreal injection of Lin⁻ HSCs results in concomitant retinal vascular and neuronal rescue in retinas of rd1/rd1 mice. Injected cells were not observed in the ONL or any place other than within, or in close proximity to, retinal blood vessels.

Functional Rescue of Lin⁻ HSC-Injected rd/rd Retinas

Electroretinograms (ERGs) were performed on mice 2 months after injection of control cells or murine Lin⁻ HSCs (FIG. 17). Immunohistochemical and microscopic analysis was done with each eye following ERG recordings to confirm that vascular and neuronal rescue had occurred. Representative ERG recordings from treated, rescued and control, non-rescued eyes show that in the rescued eyes, the digitally subtracted signal (treated minus untreated eyes) produced a clearly detectable signal with an amplitude on the order of 8-10 microvolts (FIG. 17). Clearly, the signals from both eyes are severely abnormal. However, consistent and detectable ERGs were recordable from the Lin⁻ HSC-treated eyes. In all cases the ERG from the control eye was non-detectable. While the amplitudes of the signals in rescued eyes were considerably lower than normal, the signals were consistently observed whenever there was histological rescue and were on the order of magnitude of those reported by other, gene based, rescue studies. Overall these results are demonstrate of some degree of functional rescue in the eyes treated with the Lin⁻ HSCs of the invention.

Human Bone Marrow (hBM)-Derived Lin⁻ HSCs Also Rescue Degenerating Retinas

Lin⁻ HSCs isolated from human bone marrow behave similarly to murine Lin⁻ HSCs. Bone marrow was collected from human donors and the Lin⁺ HSCs were depleted, producing a population of human Lin⁻ HSCs (hLin⁻ HSCs). These cells were labeled ex-vivo with fluorescent dye and injected into C3SnSmn.CB17-Prkdc SCID mouse eyes. The injected hLin⁻ HSCs migrated to, and targeted, sites of retinal angiogenesis in a fashion identical to that observed when murine Lin⁻ HSCs were injected (FIG. 18A). In addition to the vascular targeting, the human Lin⁻ HSCs also provided a robust rescue effect on both the vascular and neuronal cell layers of the rd1/rd1 mice (FIGS. 18B and 18C). This observation confirms the presence of cells in human bone marrow that target retinal vasculature and can prevent retinal degeneration.

Lin⁻ HSCs have Vasculo- and Neurotrophic Effects in the rd10/rd10 Mouse

While the rd1/rd1 mouse is the most widely used and best characterized model for retinal degeneration (Chang et al. 2002, Vision Res. 42:517-525), the degeneration is very rapid and in this regard differs from the usual, slower time course observed in the human disease. In this strain, photoreceptor cell degeneration begins around P8, a time when the retinal vasculature is still rapidly expanding (FIG. 15). Subsequent degeneration of the deep retinal vasculature occurs even while the intermediate plexus is still forming and, thus, the retinas of rd1/rd1 mice never completely develops, unlike that observed in most humans with this disease. An rd10 mouse model, which has a slower time course of degeneration and more closely resembles the human retinal degenerative condition, was used to investigate Lin⁻ HSC-mediated vascular rescue. In the rd10 mouse, photoreceptor cell degeneration begins around P21 and vascular degeneration begins shortly thereafter.

Since normal neurosensory retinal development is largely complete by P21, the degeneration is observed to start after the retina has completed differentiation and in this way is more analogous to human retinal degenerations than the rd1/rd1 mouse model. Lin⁻ HSCs or control cells from rd10 mice were injected into P6 eyes and the retinas were evaluated at varying time points. At P21 the retinas from both Lin⁻ HSC and control cell-injected eyes appeared normal with complete development of all vascular layers and normal development of the INL and ONL (FIGS. 18D and 18H). At approximately P21 the retinal degeneration began and progressed with age. By P30, the control cell-injected retinas exhibited severe vascular and neuronal degeneration (FIG. 18I), while the Lin⁻ HSC-injected retinas maintained nearly normal vascular layers and photoreceptor cells (FIG. 18E). The difference between the rescued and non-rescued eyes was more pronounced at later time points (compare FIGS. 18F and 18G to 18J and 18K). In the control treated eyes, the progression of vascular degeneration was very clearly observed by immunohistochemical staining for CD31 and collagen IV (FIG. 18I-K). The control-treated eyes were nearly completely negative for CD31, whereas collagen IV-positive vascular “tracks” remained evident, indicating that vascular regression, rather than incomplete vascular formation, had occurred. In contrast, Lin⁻ HSC-treated eyes had both CD31 and collagen IV-positive vessels that appeared very similar to normal, wild-type eyes (compare FIGS. 18F and 18I).

Gene Expression Analysis of rd/rd Mouse Retinas after Lin⁻ HSC Treatment

Large scale genomics (microarray analysis) was used to analyze rescued and non-rescued retinas to identify putative mediators of neurotrophic rescue. Gene expression in rd1/rd1 mouse retinas treated with Lin⁻ HSCs was compared to uninjected retinas as well as retinas injected with control cells (CD31⁻). These comparisons were each done in triplicate. To be considered present, genes were required to have expression levels at least 2-fold higher than background levels in all three triplicates. Genes that were upregulated 3-fold in Lin⁻ HSC-protected retinas compared to control cell-injected and non-injected rd/rd mouse retinas are shown in FIG. 20, panels A and B. Many of the significantly upregulated genes, including MAD and Ying Yang-1 (YY-1), encode proteins with functions involving the protection of cells from apoptosis. A number of crystallin genes, which have sequence homology and similar functions to known heat-shock proteins involving protection of cells from stress, were also upregulated by Lin⁻ HSC treated retinas. Expression of α-crystallin was localized to the ONL by immunohistochemical analysis (FIG. 19).

Messenger RNA from rd1/rd1 mouse retinas rescued with human Lin⁻ HSCs were hybridized to human specific Affymetrix U133A microarray chips. After stringent analysis, a number of genes were found whose mRNA expression was human specific, above background, and significantly higher in the human Lin⁻ HSC rescued retinas compared to the murine Lin⁻ HSC rescued retinas and the human control cell-injected non-rescued retinas (FIG. 20, panel C). CD6, a cell adhesion molecule expressed at the surface of primitive and newly differentiated CD34+ hematopoietic stem cells, and interferon alpha 13, another gene expressed by hematopoietic stem cells, were both found by the microarray bioinformatics technique, validating the evaluation protocol. In addition, several growth factors and neurotrophic factors were expressed above background by human Lin⁻ HSC rescued mouse retina samples (FIG. 20, panel D).

DISCUSSION

Markers for lineage-committed hematopoietic cells were used to negatively select a population of bone marrow-derived Lin⁻ HSC containing EPC. While the sub-population of bone marrow-derived Lin⁻ HSC that can serve as EPC is not characterized by commonly used cell surface markers, the behavior of these cells in developing or injured retinal vasculature is entirely different than that observed for Lin⁺ or adult endothelial cell populations. These cells selectively target to sites of retinal angiogenesis and participate in the formation of patent blood vessels.

Inherited retinal degenerative diseases are often accompanied by loss of retinal vasculature. Effective treatment of such diseases requires restoration of function as well as maintenance of complex tissue architecture. While several recent studies have explored the use of cell-based delivery of trophic factors or stem cells themselves, some combination of both may be necessary. For example, use of growth factor therapy to treat retinal degenerative disease resulted in unregulated overgrowth of blood vessels resulting in severe disruption of the normal retinal tissue architecture. The use of neural or retinal stem cells to treat retinal degenerative disease may reconstitute neuronal function, but a functional vasculature will also be necessary to maintain retinal functional integrity. Incorporation of cells from a Lin⁻ HSCs of the present invention into the retinal vessels of rd/rd mice stabilized the degenerative vasculature without disrupting retinal structure. This rescue effect was also observed when the cells were injected into P15 rd/rd mice. Since vascular degeneration begins on P16 in rd/rd mice, this observation expands the therapeutic window for effective Lin⁻ HSC treatment. Retinal neurons and photoreceptors are preserved and visual function is maintained in eyes injected with the Lin⁻ HSC of the present invention.

Adult bone marrow-derived Lin⁻ HSCs exert profound vasculo- and neurotrophic effects when injected intravitreally into mice with retinal degenerative disease. This rescue effect persists for up to 6 months after treatment and is most efficacious when the Lin⁻ HSCs are injected prior to complete retinal degeneration (up to 16 days after birth in mice that ordinarily exhibit complete retinal degeneration by 30 days postnatally). This rescue is observed in 2 mouse models of retinal degeneration and, remarkably, can be accomplished with adult human bone marrow-derived HSCs when the recipient is an immunodeficient rodent with retinal degeneration (e.g., the SCID mouse) or when the donor is a mouse with retinal degeneration. While several recent reports have described a partial phenotypic rescue in mice or dogs with retinal degeneration after viral based gene rescue with the wild type gene (Ali, et al. 2000, Nat Genet. 25:306-310; Takahashi et al. 1999, J. Virol. 73:7812-7816; Acland et al. 2001, Nat. Genet. 28:92-95.), the present invention is the first generic cell-based therapeutic effect achieved by vascular rescue. Thus, the potential utility of such an approach in treating a group of diseases (e.g., retinitis pigmentosa) with over 100 known associated mutations is more practical than creating individual gene therapies to treat each known mutation.

The precise molecular basis of the neurotrophic rescue effect remains unknown, but is observed only when there is concomitant vascular stabilization/rescue. The presence of injected stem cells, per se, is not sufficient to generate a neurotrophic rescue and the clear absence of stem cell-derived neurons in the outer nuclear layer rules out the possibility that the injected cells are transforming into photoreceptors. Data obtained by microarray gene expression analysis demonstrated a significant up-regulation of genes known to have anti-apoptotic effects. Since most neuronal death observed in retinal degenerations is by apoptosis, such protection may be of great therapeutic benefit in prolonging the life of photoreceptors and other neurons critical to visual function in these diseases. C-myc is a transcription factor that participates in apoptosis by upregulation various downstream apoptosis-inducing factors. C-myc expression was increased 4.5 fold in rd/rd mice over wild-type indicating potential involvement in the photoreceptor degeneration observed in the rd1/rd1 mouse. Mad1 and YY-1, two genes dramatically upregulated in Lin⁻ HSC-protected retinas (FIG. 20, panel A), are known to suppress the activity of c-myc, thus inhibiting c-myc induced apoptosis. Overexpression of Mad1 has also been shown to suppress Fas-induced activation of caspase-8, another critical component of the apoptotic pathway. Upregulation of these two molecules may play a role in protection of the retina from vascular and neural degeneration by preventing the initiation of apoptosis that normally leads to degeneration in rd/rd mice.

Another set of genes that were greatly upregulated in Lin⁻ HSC protected retinas includes members of the crystallin family (FIG. 20, panel B). Similar to heat-shock and other stress-induced proteins, crystallins may be activated by retinal stress and provide a protective effect against apoptosis. Abnormally low expression of αA-crystallins is correlated with photoreceptor loss in a rat model of retinal dystrophy and a recent proteomic analysis of the retina in the rd/rd mouse demonstrated induction of crystalline up-regulation in response to retinal degeneration. Based on our microarray data of EPC-rescued rd/rd mouse retinas, upregulation of crystallins appear to play a key role in EPC mediated retinal neuroprotection.

Genes such as c-myc, Mad1, Yx-1 and the crystallins are likely to be downstream mediators of neuronal rescue. Neurotrophic agents can regulate anti-apoptotic gene expression, although our microarray analysis of retinas rescued with mouse stem cells did not demonstrate induction of increased levels of known neurotrophic factors. Analysis of human bone marrow-derived stem cell-mediated rescue with human specific chips did, on the other hand, demonstrate low, but significant increases in the expression of multiple growth factor genes.

The upregulated genes include several members of the fibroblast growth factor family and otoferlin. Mutations in the otoferlin gene are associated with genetic disorders leading to deafness due to auditory neuropathy. It is possible that otoferlin production by injected Lin⁻ HSCs contributes to the prevention of retinal neuropathy as well. Historically, it has long been assumed that vascular changes observed in patients and animals with retinal degeneration were secondary to decreased metabolic demand as the photoreceptors die. The present data indicate that, at least for mice with inherited retinal degeneration, preserving normal vasculature can help maintain components of the outer nuclear layer as well. Recent reports in the literature would support the concept that tissue-specific vasculature has trophic effects that go beyond that expected from simply providing vascular “nourishment.” For example, liver endothelial cells can be induced to produce, after VEGFR1 activation, growth factors critical to hepatocyte regeneration and maintenance in the face of hepatic injury (LeCouter et al. 2003, Science 299:890-893).

Similar indicative interactions between vascular endothelial cells and adjacent hepatic parenchymal cells are reportedly involved in liver organogenesis, well before the formation of functional blood vessels. Endogenous retinal vasculature in individuals with retinal degeneration may not facilitate so dramatic a rescue, but if this vasculature is buttressed with endothelial progenitors derived from bone marrow hematopoietic stem cell populations, they may make the vasculature more resistant to degeneration and at the same time facilitate retinal neuronal, as well as vascular, survival. In humans with retinal degeneration, delaying the onset of complete retinal degeneration may provide years of additional sight. The animals treated with the Lin⁻ HSCs of the present invention had significant preservation of an ERG, which may be sufficient to support vision.

Clinically, it is widely appreciated that there can be substantial loss of photoreceptors and other neurons while still preserving functional vision. At some point, the critical threshold is crossed and vision is lost. Since nearly all of the human inherited retinal degenerations are of early, but slow, onset, it may be possible to identify an individual with retinal degeneration, treat them intravitreally with an autologous bone marrow stem cell graft and delay retinal degeneration with concomitant loss of vision. To enhance targeting and incorporation of these stem cells, the presence of activated astrocytes would be desirable. This can be accomplished by early treatment when there is an associated gliosis or by using a laser to stimulate local proliferation of activated astrocytes.

The Lin⁻ HSC populations of the present invention contain a population of EPC that can promote angiogenesis by targeting reactive astrocytes and incorporate into an established template without disrupting retinal structure. The Lin⁻ HSC of the present invention also provide a surprising long-term neurotrophic rescue effect in eyes suffering from retinal degeneration. In addition, genetically modified, autologous Lin⁻ HSC compositions containing EPC can be transplanted into ischemic or abnormally vascularized eyes and can stably incorporate into new vessels and continuously deliver therapeutic molecules locally for prolonged periods of time. Such local delivery of genes that express pharmacological agents in physiologically meaningful doses represents a new paradigm for treating currently untreatable ocular diseases.

Numerous variations and modifications of the embodiments described above may be effected without departing from the spirit and scope of the novel features of the invention. No limitations with respect to the specific embodiments illustrated herein are intended or should be inferred. 

1. A method of isolating an adult bone marrow-derived, lineage negative hematopoietic stem population including endothelial progenitor cells comprising the steps of: (a) extracting bone marrow from an adult mammal; (b) separating a plurality of monocytes from the bone marrow; (c) labeling the monocytes with biotin-conjugated lineage panel antibodies to one or more lineage surface antigens selected from the group consisting of CD2, CD3, CD4, CD11, CD11a, Mac-1, CD14, CD16, CD19, CD24, CD33, CD36, CD38, CD45, Ly-6G, TER-119, CD45RA, CD56, CD64, CD68, CD86, CD66b, HLA-DR, and CD235a; (d) removing monocytes that are positive for said one or more lineage surface antigens from the plurality of monocytes and recovering a population of lineage negative hematopoietic stem cells containing endothelial progenitor cells.
 2. The method of claim 1 wherein the mammal is a human.
 3. The method of claim 1 wherein the mammal is a human and the monocytes are labeled in step (c) with biotin-conjugated lineage panel antibodies to CD2, CD3, CD4, CD11a, Mac-1, CD14, CD16, CD19, CD33, CD38, CD45RA, CD64, CD68, CD86, and CD235a.
 4. The method of claim 2 wherein the mammal is a human and the method includes the additional steps of labeling the monocytes with a biotin-conjugated CD133 antibody and recovering a population of CD133 positive, lineage negative hematopoietic stem cells.
 5. The method of claim 2 wherein the mammal is a human and the method includes the additional steps of labeling the monocytes with a biotin-conjugated CD133 antibody, removing CD133 positive cells, and recovering a population of CD133 negative, lineage negative hematopoietic stem cells.
 6. A hematopoietic stem cell population isolated by the method of claim
 1. 7. A method of enhancing retinal neovascularization in a mammal comprising intravitreally injecting lineage negative hematopoietic stem cell population of claim 6 into the eye of a mammal in need of retinal neovascularization wherein the stem cells are derived from bone marrow of the same species of mammal as the species into whose eye the cells are injected.
 8. The method of claim 7 wherein the stem cells are derived from the bone marrow of the same individual mammal into whose eye the stem cells are injected.
 9. The method of claim 7 wherein the mammal is a human.
 10. A method of treating an ocular disease in a mammal comprising isolating from the bone marrow of the mammal a lineage negative hematopoietic stem cell population that includes endothelial progenitor cells by: (a) extracting bone marrow from a mammal suffering from an ocular disease; (b) separating a plurality of monocytes from the bone marrow; (c) labeling the monocytes with biotin-conjugated lineage panel antibodies to one or more lineage surface antigens selected from the group consisting of CD2, CD3, CD4, CD11, CD11a, Mac-1, CD14, CD16, CD19, CD24, CD33, CD36, CD38, CD45, Ly-6G, TER-119, CD45RA, CD56, CD64, CD68, CD86, CD66b, HLA-DR, and CD235a; (d) separating monocytes that are positive for said one or more lineage surface antigens from the plurality of monocytes and recovering a population of lineage negative hematopoietic stem cells containing endothelial progenitor cells; and subsequently intravitreally injecting the isolated stem cells into an eye of the mammal in a number sufficient to ameliorate the effects of the disease.
 11. The method of claim 10 wherein the number of stem cells is effective for repairing retinal damage of the mammal's eye.
 12. The method of claim 10 wherein the number of stem cells is effective for stabilizing retinal neovasculature of the mammal's eye.
 13. The method of claim 10 wherein the number of stem cells is effective for maturing retinal neovasculature of the mammal's eye.
 14. A transfected lineage negative hematopoietic stem cell population comprising a stem cell population of claim 6 transfected with a gene that operably encodes a therapeutically useful peptide.
 15. The transfected stem cell population of claim 14 wherein the therapeutically useful peptide is an anti-angiogenic peptide.
 16. The transfected stem cell population of claim 14 wherein the anti-angiogenic peptide is a protein fragment.
 17. The transfected stem cell population of claim 14 wherein the therapeutically useful peptide is a neurotrophic agent.
 18. The transfected stem cell population of claim 17 wherein the neurotrophic agent is selected form the group consisting of nerve growth factor, neurotrophin-3, neurotrophin-4, neurotrophin-5, ciliary neurotrophic factor, retinal pigmented epithelium-derived neurotrophic factor, insulin-like growth factor, glial cell line-derived neurotrophic factor, and brain-derived neurotrophic factor.
 19. A method of inhibiting retinal angiogenesis in the eye of a mammal comprising intravitreally injecting a transfected stem cell population according to claim 15 into the eye of the mammal.
 20. A method of inhibiting retinal neuronal degeneration in the eye of a mammal comprising intravitreally injecting a transfected stem cell population according to claim 17 into the eye of the mammal.
 21. A transfected lineage negative hematopoietic stem cell population prepared by: (a) extracting bone marrow from an adult mammal; (b) separating a plurality of monocytes from the bone marrow; (c) labeling the plurality of monocytes with biotin-conjugated lineage panel antibodies to CD2, CD3, CD4, CD11, CD11a, Mac-1, CD14, CD16, CD19, CD24, CD33, CD36, CD38, CD45, Ly-6G, TER-119, CD45RA, CD56, CD64, CD68, CD86, CD66b, HLA-DR, and CD235a; (d) separating monocytes that are positive for said one or more lineage surface antigens from the plurality of monocytes and recovering a population of lineage negative hematopoietic stem cells containing endothelial progenitor cells; and (e) transfecting the lineage negative hematopoietic stem cells recovered in step (d) with a polynucleotide that operably encodes a therapeutically useful peptide.
 22. The transfected stem cell population of claim 21 wherein the therapeutically useful peptide is an anti-angiogenic peptide.
 23. The transfected stem cell population of claim 21 wherein the therapeutically useful peptide is a neurotrophic agent.
 24. A method of delivering transgenes to the retinal vasculature of a mammal comprising intravitreally injecting a transfected lineage negative hematopoietic stem cell population of claim 14 into the eye of the mammal.
 25. A method of delivering transgenes to the retinal vasculature of a mammal comprising intravitreally injecting a transfected lineage negative hematopoietic stem cell population of claim 21 into the eye of the mammal.
 26. A method of rescuing neuronal networks in the eye of a mammal comprising intravitreally injecting a transfected lineage negative hematopoietic stem cell population of claim 6 into the eye of the mammal.
 27. A method of rescuing blood vessels in the eye of a mammal comprising intravitreally injecting a transfected lineage negative hematopoietic stem cell population of claim 6 into the eye of the mammal.
 28. A method of stimulating upregulation of anti-apoptotic genes in the eye of a mammal comprising intravitreally injecting a lineage negative hematopoietic stem cell population of claim 6 into the eye of the mammal.
 29. A method of repairing ischemic tissue in the eye of a mammal comprising intravitreally injecting a lineage negative hematopoietic stem cell population of claim 6 into the eye of the mammal.
 30. A method of targeted delivery of stem cells to astrocytes in the eye of a mammal comprising intravitreally injecting a lineage negative hematopoietic stem cell population of claim 6 into the eye of the mammal.
 31. A method of targeted delivery of transgenes to astrocytes in the eye of a mammal comprising intravitreally injecting a lineage negative hematopoietic stem cell population of claim 14 into the eye of the mammal. 